BR112015004487B1 - method for preparing d, l-methionine - Google Patents

Abstract

clean method to prepare d, l-methionine. in the present invention, a clean method for preparing a d, 1-methionine is described comprising the steps of: preparing a potassium cyanide solution using a crystallized mother liquor containing calcium carbonate as an absorbent liquid to absorb hydrocyanic acid, then reacting to potassium cyanide solution with 3-methylthio propionaldehyde and ammonium bicarbonate solution at 50-150 ° C for 3-15 minutes in order to obtain a solution of 5- (j3-methylthioethyl) glycolurea, then bring the solution of 5 - (3-methylthioethyl) glycolurea at a temperature of 140-220 ° c and subject to a saponification reaction for 2-5 minutes, after the completion of the saponification, reducing the temperature to 140-220 ° c and subject to a saponification reaction by 2-5minutes, after the completion of the saponification, reducing the temperature to 0-40 ° c, extract with an organic solvent, neutralize the aqueous phase with co2 and crystallize, then filter, wash, and dry to obtain a powder. acceptable d, l-methionine product; bring the mother liquor of d, l-methionine from the filtration at a temperature of 110-160 ° C to remove co2, which are all then circulated and used as a hydrocyanic acid absorption liquid. the process path of the present invention is a suitable path for clean, continuous production, substantially without producing waste water and waste gas.

Description

METHOD FOR PREPARING D, L-METHIONINE

TECHNICAL FIELD [001] The present invention is related to the compound synthesis field, more specifically, a clean method for the preparation of D, L-methionine.

BACKGROUND OF THE INVENTION [002] D, L-methionine is an essential sulfur-containing amino acid for the human body and is closely related to the metabolism of various sulfur-containing compounds in biological organisms. Methionine belongs to the first restrictive amino acid and cannot be synthesized inside the animal's body and must be ingested with food. The addition of methionine to food products can promote the growth of farm animals, increase the percentage of lean meat, and shorten the feeding cycle. Methionine can also be used for the prevention and treatment of liver diseases, such as liver cirrhosis and chronic or acute hepatitis, because the methyl group contained in methionine can be used for the methylation of toxic products or drugs and thus have the effect detoxification. Methionine can also be used to reduce the toxic reaction of dangerous substances, such as arsenic, trichloride, carbon tetrachloride, benzene, pyridine and quinoline. According to the relevant statistical information, the market demand for methionine worldwide has reached 1,000,000 ton / year. Demand for methionine in the international market is increasing at a year-on-year growth rate of 4% in recent years; whereas demand in China is increasing at a 7% year-on-year growth rate.

[003] As introduced in the relevant literature, there are the following methods for the synthesis of D, L-methionine:

[004] On patent publication with publication number

CN1923807A, Sumitomo Chemical Co., Ltd. of Japan proposes to prepare D, L

Petition 870190088055, of 9/6/2019, p. 9/38 / 25 methionine through hydrolysis of 5- (β-methylthioethyl) glycolurea with alkaline potassium compounds, then acidification with pressurized CO2 gas and then crystallization and fractional condensation, with the addition of polyvinyl alcohol. Although this method can recycle CO2 gas, due to the artificial addition of polyvinyl alcohol, the mother liquor solution as discharged cannot be recycled and can only be discarded, which produces a large amount of waste water with organic compounds containing N and S. In addition, the fractional condensation method consumes a large amount of thermal energy to the extent of resulting in a significant increase in the cost of the product of D, Lmethionine.

[005] On patent publication with publication number

CN85108505A, Wang Jianhua proposes the addition of a mixture of neutral amino acids and organic acids, containing 10% acrolein, as a catalyst, during the preparation of 5- (β-methylthioethyl) glycolurea; it is intended to prepare 5- (β-methylthioethyl) glycolurea with a one-step method using methanethiol and acrolein, to simplify the operation process, and to improve the yield of the preparation of 5- (β-methylthioethyl) glycolurea. However, a mixture of neutral amino acid and organic acid that is added intentionally for later saponification with the addition of alkaline substances inevitably participates in the reaction, and produces the metal salt. As a result, metal salts have accumulated in the stock solution so that the stock solution cannot be recycled and produces a large amount of waste water with organic compounds containing N and S.

[006] In patent publication with publication number

CN85108531A, Wang Jianhua proposes to produce D, L-methionine through saponification of 5- (β-methylthioethyl) glycolurea with alkaline sodium compounds, acidification with vitriol and separation with crystallization and fractional condensation method. Such a method can produce a large amount of

Petition 870190088055, of 9/6/2019, p. 10/38 / 25 by-products, such as sodium sulfate, separation and processing of sodium sulfate become a significant burden for production.

[007] In patent publication with publication number

CN1589259A, to obtain a methionine preparation method that can produce a high quality, bulk density, granular or tabular methionine crystal in a stable manner, Nippon Soda Co., Ltd. proposes the use of an intermetallic compound selected from hydroxide metal, metal carbonate or a metal carbonate salt to hydrolyze 5- (βmethylthioethyl) glycolurea to obtain the methionine metal salt, then neutralize the methionine metal salt using the pressurized CO2 gas to perform the crystallization of methionine. Thereafter, the methionine is separated from the filtrate, and it is ensured that the filtrate can be recycled for the hydrolysis of 5- (β-methylthioethyl) glycolurea during the preparation of methionine. According to this method, despite the fact that the partial mother solution for crystallization is again used for hydrolysis, some residues and by-products are not eliminated during the intermediate process and are inevitably accumulated as it affects the application effect and the product quality. However, since the stock solution is not used for the preparation of 5- (β-methylthioethyl) glycolurea, a large amount of water is required, making it impossible for the amount of water to be balanced throughout the process. In addition, each use will consume a large amount of water as required by the preparation of 5- (βmethylthioethyl) glycolurea.

[008] In patent publication with publication number

CN1103066A, Degussa AG proposes a synthesis technique to obtain an amino nitrile compound through a reaction between methylthio propionaldehyde, HCN and ammonia, and hydrolyze the amino nitrile compound with a ketone catalyst to obtain the aminoamide, and then , finally prepare methionine by hydrolysis at high temperature with an alkaline catalyst.

Petition 870190088055, of 9/6/2019, p. 11/38 / 25

Such method of synthesis of methionine also has some defects, despite the fact that it is provided with the original characteristics in comparison with the industrial production method. The most serious defect lies in the large amount of waste water as produced; for example, aminoamide obtained by adding ketone catalyst during its preparation must subject separation and purification by passing through a column, such a separation and purification method is unsuitable for such a volume product during industrial production. Seen from general techniques, this does not solve the problem of a large amount of wastewater.

[009] On patent publication with publication number

CN102399177A, Li Kuanyi proposes a method of green and clean technique for the continuous synthesis of methionine: having methylthional propionaldehyde as synthesized with acrolein and methanthiol as the material for the reaction with hydrogen cyanide to obtain the intermediate 2-hydroxy -4- (methylthio- ) nitrile; obtaining additional hydantoin solution through continuous reaction of the intermediate 2-hydroxy-4- (methylthio) nitrile in the first reaction bed of the combined reactor in the presence of excess ammonia and carbon dioxide. The hydantoin solution will flow out of the first reaction bed, and release excess carbon dioxide and ammonia into the desorption column. The subjection of the hydantoin solution to the desorption will flow in the second reaction bed of the combined reactor for hydrolysis under alkaline conditions to obtain the potassium methionine solution. The solution of methionine potassium with carbon dioxide are neutralized to obtain a solution of potassium hydrogen carbonate and methionine. Methionine is separated from the solution by crystallization; whereas potassium hydrogen carbonate and mother solution must be treated for recycling. It seems that this technical approach is extremely clean and suitable for industrialized production. However, according to its patent introduction and analysis from the point of view of industrialized production, it still has

Petition 870190088055, of 9/6/2019, p. 12/38 / 25 some disadvantages. First, this technique requires a large amount of water for the reaction during the preparation of the hydantoin solution; whereas the mother crystallization solution is used for hydrolysis with the exception of hydantoin preparation. As a result, a large amount of water is distilled to prepare hydantoin during hydrolysis to additionally apply the remaining stock solution for hydantoin hydrolysis. This process results in increased production costs, as it requires a large amount of thermal and electrical energy. Second, delayed elimination of by-products such as that produced during the chemical reaction throughout the technological process can seriously affect the quality of the final products, making it more difficult to purify the final products. However, it also affects the consumption and batch of the mother solution. This results in an increase in the emission of wastewater during industrialized production.

[0010] As proposed in US2004 / 0039228A1, D, L-methionine can be obtained through the reaction between some mother solution of crystallization, a certain amount of NH3 and CO2 at a temperature of 60 ° C in the presence of TiO2, the catalyst, saponification at 180 to 300 ° C and neutralization with CO2. Despite the fact that such a method makes use of the partial crystallization mother solution indiscriminately to minimize the emission of wastewater, it will result in the following problems due to the addition of TiO2 as a catalyst in the technological process: if the entire mother crystallization solution is used indiscriminately, will result in TiO2 accumulation; In addition, D, L-methionine subject to crystallization and filtration will also contain TiO2 and, thus, the product will contain metallic Ti which will result in the reduction of product quality, which makes the follow-up treatment more complicated and difficult.

[0011] In patent publication with publication number EB1761074A1 (CN101602700A), Sumitomo Chemical invokes the following

Petition 870190088055, of 9/6/2019, p. 13/38 / 25 method: use of the alkaline potassium compound as the catalyst for the saponification of 5- (β-methylthioethyl) glycolurea; use of CO2 for neutralization and crystallization; use of a mother crystallization solution subjecting to the concentration and fractional crystallization mentioned above for saponification of reaction fluid of 5- (β-methylthioethyl) glycolurea following indiscriminately; addition of polyvinyl alcohol in the remaining mother solution subjecting to the secondary concentration for crystallization. At this point, the parent solution is abandoned with the exception of indiscriminate use. This technique is used by Sumitomo Chemical for industrial production of D, L-methionine. However, there are many problems with this technique, especially in the aspect of green and clean production. Only partial crystallization stock solution is used. Most of the mother crystallization solution is abandoned after a period of use, which produces a large amount of waste water.

SUMMARY OF THE INVENTION [0012] In view of an excessive amount of waste water with organic compounds containing N and S - produced during the industrialized production of D, L-methionine and serious environmental pollution, a major technical problem solved by the present invention is that of provide a method of preparing D, L-methionine, which is clean and easy to operate.

[0013] For this purpose, the present invention provides a clean method for the preparation of D, L-methionine, which comprises the following steps:

(1) prepare a 5- (e-methylthioethyl) glycolurea reaction fluid using 3-methylthio propionaldehyde, KCN and NH4HCO3 solutions as raw materials for continuous reaction in the tubular reactor which is gradually heated;

(2) decompress the 5- (e-methylthioethyl) glycolurea reaction fluid to separate NH3 and CO2 to dispense to another tubular reactor

Petition 870190088055, of 9/6/2019, p. 14/38 / 25 for decomposition and saponification to obtain a saponification reaction fluid;

(3) eliminate NH3 and CO2 produced during saponification by desorption of the saponification fluid to obtain a solution of D, L-methionine potassium;

(4) obtain a solution of NH4HCO3 by spraying water and absorbing NH3 and CO2 when separated in steps (2) and (3), and directly use the NH4HCO3 solution as a material for preparing the reaction fluid of 5 - (3-methylthioethyl) glycolurea in step (1);

(5) cool the L-methionine potassium solution in step (3), and then use an organic solvent for continuous and reverse extraction; directly using a recycled organic solvent by distilling an organic solvent layer for continuous and reverse extraction; the raffinate produced by distillation being treated as a residual fluid;

(6) dispense water that is produced by continuous and countercurrent extraction in step (5) for a continuous crystallizer, while dispensing CO2 gas for the continuous crystallizer for acidification to control the PH value of the reaction fluid in the continuous crystallizer in 6-9, and then obtain a crystallization mix;

(7) separating solid and liquid in the crystallization intermix to obtain crude D, L-methionine product and a crystallization stock solution; washing crude D, L-methionine product with water for solid-liquid separation to obtain a D, L-methionine filter cake and washing filtrate;

(8) drying the D, L-methionine filter cake under the protection of an inert gas to obtain D, L-methionine product;

(9) combining the mother liquor solution and the washing filtrate from step (7) for dispensing to a decomposition column to fully decompose KHCO3 into K2CO3 to release CO2 gas; the gas

Petition 870190088055, of 9/6/2019, p. 15/38 / 25

Released CO2 that is subjected to compression is dispensed to the continuous crystallizer by acidification and crystallization;

(10) use the stock solution containing K2CO3 as obtained in step (9) for absorbing HCN gas to prepare a solution of KCN which is the material for preparing 5- (3-methylthioethyl) glycolurea in step (1).

[0014] In step (1), the preferred molar ratio of 3-methylthio propionaldehyde, KCN and NH4HCO3 is 1: 1 to 1.1: 2 to 3. At this point, an optimal single-pass conversion rate of 3-methylthio propionaldehyde and an equipment usage fee can be obtained.

[0015] In step (1), the preferred range is the gradual heating from 50 to 150 ° C with a reaction time of up to 3 to 15 minutes.

[0016] In step (2), the preferred temperature for decomposition and saponification is 140 to 220 ° C, with a time of up to 2 to 15 minutes.

[0017] In step (5), the solution temperature of D, L-methionine potassium is reduced to 0 to 40 ° C before using an organic solvent equivalent to 0.5 to 2 times the weight of the solution of D, L - potassium methionine for continuous and reverse extraction.

[0018] In step (5), preferred organic solvents for continuous and reverse extraction include one or more of toluene, ethylbenzene, dimethylbenzene, n-butyl alcohol, isobutanol, n-pentanol, 2-methyl-1-butanol, isoamylol , sec- amyl alcohol, 3-pentanol, tert-amyl alcohol, nhexyl alcohol, 4-methyl-2-pentanol, 2-ethyl alcohol, 2-methyl amyl alcohol, heptanol,

2-heptanol, 3-heptanol, 2-ethylhexyl alcohol, 2-octanol ether, octanol, 3,5,5-trimethylhexanol, ether, MTBE (methyl-tert-butyl ether), isopropyl ether, npropyl, n-butyl, ether isoamyl, hexyl ether, 2-methyl tetrahydrofuran, anisol, ethoxybenzene, 3-methylanisole, EBE (benzyl ether acetate), ethylene glycol diethyl ether, ethylene glycol dipropyl ether and diethylene glycol dipropyl ether.

[0019] Some viscous oil-soluble by-products can be

Petition 870190088055, of 9/6/2019, p. 16/38

9/25 produced during the preparation of 5- (β-methylthioethyl) glycolurea and D, Lmethionine potassium. These by-products can be extracted by the organic solvents mentioned above; whereas D, L-methionine is a substance highly soluble in water, which is unlikely to dissolve in the organic solvents mentioned above. Therefore, by-products are eliminated over time through extraction by organic solvents.

[0020] In step (6), the temperature of continuous crystallization is from 0 to 40 ° C; whereas the reaction fluid is to stay inside the continuous crystallizer for 0.5 to 5 hours.

[0021] In step (9), the temperature and pressure of the decomposition column are 110 to 160 ° C and 0.15 to 0.8 MPa with decomposition reaction time up to 1 to 4 hours.

[0022] The reaction formula in step (1) is:

+ KCN

+ 2NHíHCQ, ---- ►

K1ICQ, + MH, + 2H /) [0023]

The reaction formulas in steps (2) and (3) are:

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10/25

KFICOK-, CO ₅

Η-ιί) [0024]

The reaction formula in step (4) is:

NH ₃ + CO ₂ + H ₂ O ---- NHjHCOj [0025] The reaction formula in step (6) is:

+ CO; + HjO

[0026] The reaction formula in step (9) is:

2KI1CO ₅ ---- ► K-iCtta + ^ΓΟ ζ + [0027] The reaction formula in step (10) is:

---- KCN + KHCO, [0028] In step (5), the by-products produced during the reaction are eliminated by means of extraction in order to ensure the repeated and unlimited recycling of the process water.

[0029] The purpose of the present invention is to decompose KHCO3 into K2CO3 by heating, and to use mother crystallization solution containing K2CO3 as HCN absorption liquid to prepare the KCN solution. This eliminates the need to add another metal salt during

Petition 870190088055, of 9/6/2019, p. 18/38 / 25 the entire technical process, in order to lay a solid base for the recycling of process water throughout the preparation process.

[0030] To ensure a clean process, NH3 and CO2 gases produced during the preparation of 5- (β-methylthioethyl) glycolurea of the present invention and saponification are subjected to absorption in order to re-form NH4HCO3; while NH4HCO3 is a material as needed for the preparation of 5- (β-methylthioethyl) glycolurea. The objective is to guarantee the maximum use of auxiliary materials as produced during the technical process.

[0031] According to the analysis of the industrial production process, the process of preparing D, L-methionine, using methods as reported in the existing literature, can produce a large amount of waste water. In addition, organic compounds containing N and S in wastewater can cause severe environmental pollution and high process costs. The process of the present invention can prevent the production of waste water from the source. In addition, the widespread use of exhaust gases produced during production can basically prevent the production of exhaust gases during the technical process. For this reason, the D, L-methionine synthesis technique of the present invention is a clean technique approach in accommodation with industrialized production.

BRIEF DESCRIPTION OF THE DRAWINGS [0032] Fig. 1 is the flow diagram for the present invention.

[0033] In the drawing, T1 is an HCN absorption column; T2 is a CO2 and NH3 absorption column; R1 is the first tubular reactor; R2 is a pressure relief tank; R3 is the second tubular reactor; T3 is a desorption column; T4 is a continuous extraction column; T5 is an organic solvent distillation and recycling column; T6 is a continuous crystallizer; S1 is the first solid-liquid separator; R4 is a purifier; S2 is the second solid-liquid separator; T7 is a KHCO3 decomposition column.

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DETAILED DESCRIPTION OF THE INVENTION [0034] The present invention is described with reference to the following specific embodiments. These embodiments are only examples, which should not be considered as restricting the scope or method of implementation of the present invention.

Embodiment 1 [0035] A dosing liquid dispensing pump was used to dispense treated crystallization stock solution (10% K2CO3 solution was used in the initial start) for the HCN T1 absorption column at a flow of 700 kg / H. However, 5.4 kg / h of HCN gas was dispensed to the HCN absorption column for the preparation of a KCN solution in the HCN T1 absorption column, and a liquid dispensing pump was used to dispense the solution of KCN to the first tubular reactor R1. A liquid dispensing pump was used to dispense ammonium bicarbonate by absorbing ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column for the first tubular reactor R1 (16% ammonium bicarbonate solution was used in the initial start-up ) at a speed of 200 kg / h, and a liquid dispensing pump was used to supply 3-methylthio propionaldehyde to the first tubular reactor R1 at a speed of 20.8 kg / h at the same time. The reaction liquid remained for 7 minutes, respectively, at 50 ° C and 100 ° C, and remained for another 1 minute at 150 ° C. The reaction fluid discharged from the first tubular reactor R1 was subjected to decompression in the decompression tank R2 to discharge excess ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column to obtain 910 kg / h of 5- (β-methylthioethyl) glycolurea solution.

[0036] A liquid dispensing pump was used to dispense the 5- (β-methylthioethyl) glycolurea solution prepared for the second tubular reactor R3 at a speed of 910 kg / h. The reaction liquid was kept

Petition 870190088055, of 9/6/2019, p. 20/38 / 25 in the second tubular reactor for 15 minutes at 140 ° C during saponification before decompression in the T3 absorption column. The ammonia gas and carbon dioxide produced during the reaction were discharged to the CO2 absorption column and NH3 T2 for absorption. The saponification liquid was cooled to a temperature of 40 ° C in the heat exchanger, which was subsequently dispensed to the column of continuous extraction through the pump at a speed of 906 kg / h. Meanwhile, 453 kg / h of ethylene glycol dipropyl ether was dispensed to the continuous extraction column T4 for continuous reverse extraction. Continuous differential distillation of the ethylene glycol dipropyl ether layer was performed on the T5 organic solvent recycling distillation column to recycle the solvent for use circulated during the extraction process, and incinerate waste at the same time. The water layer was supplied to the continuous T6 crystallizer at a speed of 935 kg / h, and at the same time CO2 gas was dispensed to the continuous T6 crystallizer for acidification until the pH value of the reaction system was up to 8. Crystallization continuous was conducted at a temperature of 40 ° C, and the reaction liquid remained in the continuous crystallizer for 3 hours. The crystallization liquid was subjected to continuous solid-liquid centrifugal separation in the first solid-liquid separator S1 to filter crude D, L-methionine product, and prepare a mother crystallization solution for later use. The solid dispensing equipment was used to dispense crude D, L-methionine product to the R4 purifier for spiral agitation and washing in the specified amount at a rate of 34 kg / h. However, 40 kg / h of water was continuously dispensed to the R4 purifier to control the material temperature in the R4 purifier below 5 ° C. The solid material was kept in the R4 purifier for 15 minutes. The intermixture subjected to continuous stirring and washing in the R4 purifier was under continuous solid-liquid centrifugal separation through the second solid-liquid separator S2. The wash filtrate was

Petition 870190088055, of 9/6/2019, p. 21/38 / 25 poured into the mother crystallization solution, and D, L-methionine as a filtrate was air-dried at 110 ° C under the protection of N2 to obtain 27.5 kg / h of D product , Finished L-methionine. Inspection was carried out according to GB-T17810-2009 Feed Grade DL-Methionine to obtain the result that the methionine content was up to 99.5% and the total molar reaction yield based on 3-methylthional propionaldehyde was up to 92 , 3%.

[0037] The crystallization stock solution and the wash filtrate were dispensed on the KHCO3 T7 decomposition column at a speed of 977 kg / h, and remained for 1 hour at 160 ° C to fully decompose potassium hydrogen carbonate as contained in mother solution in potassium carbonate. Meanwhile, 210 kg / h of water and 45 kg / h of ethylene diglycol ether were prepared by distillation at the top of the column. The distilled water was circulated to the R4 purifier for agitation before use after 40 kg / h, while 170 kg / h of remaining distilled water was used in the CO2 and NH3 T2 absorption column. Distilled ethylene diglycol ether was circulated to the T4 extraction column for later use, while the CO2 gas discharged through the decomposition was used for acidification and crystallization in the continuous T6 crystallizer after compression. The stock solution containing potassium carbonate solution discharged from the bottom of the column was cooled before circulation to the HCN T1 absorption column for formonitrile absorption.

Embodiment 2 [0038] A dosing liquid dispensing pump was used to dispense a treated crystallization stock solution (10% K2CO3 solution was used in the initial startup) for the HCN T1 absorption column at a flow rate of 552 kg / h. However, HCN gas was dispensed to the HCN absorption column at 5.94 kg / h for the preparation of the KCN solution in the HCN T1 absorption column, and a liquid dispensing pump was

Petition 870190088055, of 9/6/2019, p. 22/38 / 25 used to dispense the KCN solution to the first tubular reactor R1. A liquid dispensing pump was used to dispense ammonium bicarbonate by absorbing ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column for the first tubular reactor R1 (16% ammonium bicarbonate solution was used in the initial start-up ) at a speed of 250 kg / h, and a liquid dispensing pump was used to supply 3-methylthio propionaldehyde to the first tubular reactor R1 at a speed of 20.8 kg / h at the same time. The reaction fluid remained for 3 minutes at 60 ° C and 120 ° C, respectively, and remained for another 1 minute at 150 ° C. The reaction fluid discharged from the first tubular reactor R1 was subjected to decompression in the decompression tank R2 to discharge excess ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column to obtain 805 kg / h solution of 5- (β-methylthioethyl) glycolurea.

[0039] A liquid dispensing pump was used to dispense the 5- (β-methylthioethyl) glycolurea solution prepared for the second tubular reactor R3 at a speed of 805 kg / h. The reaction fluid remained in the second tubular reactor for 2 minutes at 220 ° C during decompression before saponification in the T3 absorption column. Carbon dioxide and ammonia gas produced during the reaction were discharged to the CO2 absorption column and NH3 T2 for absorption. The saponification liquid was cooled to 0 ° C in the heat exchanger, which was later dispensed to a continuous extraction column T4 by means of the pump at a speed of 800 kg / h. Meanwhile, 1,600 kg / h of ethylene glycol dipropyl ether was dispensed to the continuous extraction column T4 for continuous reverse extraction. Continuous differential distillation of the ethylene glycol dipropyl ether layer was performed on the T5 organic solvent recycling distillation column to recycle the solvent for use circulated during the extraction process, and incinerate waste at the same time. The layer of

Petition 870190088055, of 9/6/2019, p. 23/38 / 25 water was supplied to the continuous crystallizer T6 at a speed of 790 kg / h, and at the same time CO2 gas was dispensed to the continuous crystallizer T6 for acidification to the pH value of the reaction system up to 6. Crystallization continuous was conducted at a temperature of 0 ° C, and the reaction liquid remained in the continuous crystallizer for 0.5 hours. The crystallization liquid was subjected to continuous solid-liquid centrifugal separation in the first solid-liquid separator S1 to filter product of D, crude Lmethionine, and the mother crystallization solution was prepared for later use. A solid dispensing equipment was used to dispense crude D, L-methionine product to the R4 purifier for spiral agitation and washing in the specified amount at the rate of 34 kg / h. Meanwhile, 102 kg / h of water was continuously dispensed to the R4 purifier and the material temperature in the R4 purifier was controlled below 0 ° C. The solid material remained in the R4 purifier for 5 minutes. The continuous solid-liquid centrifugal separation of the intermix was carried out by subjecting to continuous stirring and washing in the R4 purifier through the second solid-liquid separator S2. The wash filtrate was poured into the mother crystallization solution, and the D filter cake, L-methionine filtered at 110 ° C, was air-dried under the protection of N2 to obtain 27.2 kg / h of finished D, L-methionine product. Inspection was carried out according to GB-T17810-2009 Feed Grade DL-Methionine to obtain the results that the methionine content was up to 99.3%, and the total molar reaction yield as based on 3-methylthional propionaldehyde was up to 91.3%.

[0040] The crystallization stock solution and the wash filtrate were dispensed on the KHCO3 T7 decomposition column, at a speed of 890 kg / h, and remained for 3 hours at 130 ° C to decompose the potassium hydrogen carbonate as contained in the potassium carbonate stock solution. Meanwhile, 312 kg / h of water and 5 kg / h of toluene

Petition 870190088055, of 9/6/2019, p. 24/38 / 25 were obtained by distillation at the top of the column. 102 kg / h of distilled water was distributed to the R4 purifier for stirring before further use; while 210 kg / h of remaining distilled water was used in the CO2 and NH3 T2 absorption column. Distilled toluene was circulated to the T4 extraction column for later use; while the CO2 gas discharged through the decomposition was used for acidification and crystallization in the continuous T6 crystallizer after compression. The stock solution containing potassium carbonate solution discharged from the bottom of the column was cooled before circulation to the HCN T1 absorption column for the formonitrile absorption.

Embodiment 3 [0041] A dosing liquid dispensing pump was used to dispense the treated crystallization mother solution (10% K2CO3 solution was used in the initial start) for the HCN T1 absorption column at the flow rate of 828 kg / h. Meanwhile, 5.67 kg / h of HCN gas was dispensed into the HCN absorption column for the preparation of the KCN solution in the HCN T1 absorption column, and a liquid dispensing pump was used to dispense the solution of KCN to the first tubular reactor R1. A liquid dispensing pump was used to dispense ammonium bicarbonate by absorbing ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column for the first R1 tubular reactor (16% ammonium bicarbonate solution was used in the initial start-up ) at a speed of 300 kg / h, and a liquid dispensing pump was used to deliver 3-methylthio propionaldehyde to the first tubular reactor R1 at a speed of 20.8 kg / h at the same time. The reaction fluid remained for 1 minute and 2 minutes, respectively, at 90 ° C and 120 ° C, and remained for another 2 minutes at 150 ° C. The reaction fluid discharged from the first tubular reactor R1 was subjected to decompression in the decompression tank R2 to discharge gas from

Petition 870190088055, of 9/6/2019, p. 25/38 / 25 excess ammonia and carbon dioxide in the CO2 and NH3 T2 absorption column to obtain 1122 kg / h solution of 5- (β-methylthioethyl) glycolurea.

[0042] A liquid dispensing pump was used to dispense the 5- (β-methylthioethyl) glycolurea solution prepared for the second tubular reactor R3, at a speed of 1,122 kg / h. The reaction fluid remained in the second tubular reactor R3 for 4 minutes at 200 ° C during decompression before saponification in the T3 absorption column. The ammonia and carbon dioxide gas produced during the reaction was discharged to the CO2 and NH3 T2 absorption column for absorption. The saponification liquid was cooled to a temperature of 20 ° C in the heat exchanger, which was later dispensed to the continuous extraction column T4 by means of the pump at a speed of 1,117 kg / h. Meanwhile, 1,000 kg / h of ethylene glycol dipropyl ether was dispensed to the continuous extraction column T4 for continuous reverse extraction. Continuous differential distillation of the ethylene glycol dipropyl ether layer on the T5 organic solvent recycling distillation column was conducted to recycle the solvent for use circulated during the extraction process, and incinerate waste at the same time. The water layer was dispensed in the continuous T6 crystallizer at a speed of 1,130 kg / h and, at the same time, the CO2 gas was dispensed in the continuous T6 crystallizer for acidification until the pH value of the reaction system was up to 8. A continuous crystallization was conducted at a temperature of 20 ° C, and the reaction liquid remained in the continuous crystallizer for 5 hours. The crystallization liquid was subjected to continuous solid-liquid centrifugal separation in the first solid-liquid separator to filter crude D, L-methionine product, and crystallization stock solution was prepared for later use. The solid dispensing equipment was used to dispense crude D, L-methionine product to the R4 purifier for spiral agitation and washing in the specified amount at a rate of 35 kg / h. However, 70 kg / h of

Petition 870190088055, of 9/6/2019, p. 26/38 / 25 water was continuously dispensed to the R4 purifier to control the material temperature in the R4 purifier below 20 ° C; the solid material is to remain in the R4 purifier for 10 minutes; proceed with the continuous solid-liquid centrifugal intermixing, subjecting to continuous agitation and washing in the purifier R4 through the second solid-liquid separator S2; pour the washing filtrate into the mother crystallization solution, and proceed with the flow drying of the D, L-methionine filter cake as filtered at 140 ° C under the protection of N2 to obtain 27.9 kg / h of finished D, L-methionine product. Proceed with inspection as per GB-T17810-2009: Feed Grade DL-methionine to make sure that the methionine content is up to 99.4%, and the total molar reaction yield as based on 3-methylthio propionaldehyde is up to 93.6%.

[0043] Dispense crystallization stock solution and washing filtrate to the KHCO3 T7 decomposition column at a speed of 1.207 kg / h, and leave them to stand for 4 hours at 110 ° C to decompose the potassium hydrogen carbonate. as contained in the potassium carbonate stock solution. Meanwhile, 328 kg / h of water and 25 kg / h of amyl carbinol were prepared by distillation at the top of the column. 70 kg / h of distilled water was dispensed to the R4 purifier for stirring before additional use; while 258 kg / h of remaining distilled water was used in the CO2 and NH3 T2 absorption column. Distilled amyl carbinol was circulated in the T4 extraction column for later use; while the CO2 gas discharged through the decomposition was used for acidification and crystallization in the continuous T6 crystallizer after compression. The stock solution containing potassium carbonate solution as discharged from the bottom of the column was cooled before circulation to the HCN T1 absorption column for formonitrile absorption.

Embodiment 4 [0044] A metering liquid dispensing pump was

Petition 870190088055, of 9/6/2019, p. 27/38 / 25 used to dispense treated crystallization mother solution (10% K2CO3 solution was used in the initial start) for the HCN T1 absorption column at a flow of 700 kg / h. However, 5.4 kg / h of HCN gas was dispensed into the HCN absorption column for the preparation of the KCN solution in the HCN T1 absorption column, and a liquid dispensing pump was used to dispense the KCN to the first tubular reactor R1. A liquid dispensing pump was used to dispense ammonium bicarbonate by absorbing ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column for the first tubular reactor R1 (16% ammonium bicarbonate solution was used in the initial start-up ) at a speed of 200 kg / h, and a liquid dispensing pump was used to supply 3-methylthio propionaldehyde to the first tubular reactor R1 at a speed of 20.8 kg / h at the same time. The reaction fluid remained for the reaction for 3 minutes at a temperature of 150 ° C. The reaction fluid discharged from the first tubular reactor R1 was subjected to decompression in the decompression tank R2 to discharge excess ammonia gas and carbon dioxide to the CO2 and NH3 T2 absorption column to obtain 910 kg / h of 5- (β-methylthioethyl) glycolurea solution.

[0045] A liquid dispensing pump was used to dispense the 5- (β-methylthioethyl) glycolurea solution prepared for the second tubular reactor R3 at a speed of 910 kg / h. The reaction fluid remained in the second tubular reactor, R3, for 10 minutes at 170 ° C during decompression before saponification in the T3 absorption column. The ammonia and carbon dioxide gas produced during the reaction was discharged to the CO2 and NH3 T2 absorption column for absorption. The saponification liquid was cooled to a temperature of 10 ° C in the heat exchanger, which was later dispensed to a continuous extraction column T4 by means of the pump at a speed of 905 kg / h. Meanwhile, 905 kg / h of ethylene glycol dipropyl ether was dispensed onto the

Petition 870190088055, of 9/6/2019, p. 28/38 / 25 T4 continuous extraction for continuous reverse extraction. The continuous differential distillation of the ethylene glycol dipropyl ether layer on the T5 organic solvent recycling distillation column was conducted to recycle the solvent for use circulated during the extraction process, and incinerate waste at the same time. The water layer was supplied to the continuous crystallizer T6 at a speed of 915 kg / h, and at the same time CO2 gas was dispensed to the continuous crystallizer T6 for acidification until the pH value of the reaction system was up to 7.5. Continuous crystallization was carried out at a temperature of 10 ° C, and the reaction liquid remained in the continuous crystallizer for 2 hours. The crystallization liquid was subjected to continuous solid-liquid centrifugal separation in the first solid-liquid separator S1 to filter the crude D, L-methionine product, and the crystallization stock solution was prepared for later use. The solid dispensing equipment was used to dispense crude D, L-methionine product to the R4 purifier for spiral agitation and washing in the specified amount at a rate of 35 kg / h. However, 35 kg / h of water was continuously dispensed to the R4 purifier to control the material temperature in the R4 purifier below 10 ° C. The solid material remained in the R4 purifier for 10 minutes. The intermixture subjected to continuous stirring and washing in the R4 purifier was under continuous solid-liquid centrifugal separation through the second solid-liquid separator S2. The wash filtrate was poured into the mother crystallization solution, and the filter cake of D, L-methionine as filtrate was air-dried at 130 ° C under the protection of N2 to obtain 28.0 kg / h of finished D, L-methionine product. Inspection was performed according to GB-T17810-2009 Feed Grade DL-methionine to obtain the results that the methionine content was up to

99.2%, and the total molar reaction yield as based on 3-methylthio propionaldehyde was up to 94.0%.

[0046] The mother crystallization solution and the washing filtrate were

Petition 870190088055, of 9/6/2019, p. 29/38 / 25 dispensed to the KHCO3 T7 decomposition column, at a speed of 947 kg / h, and remained for 1.5 hours at a temperature of 150 ° C to decompose the potassium hydrogen carbonate contained in the mother solution in potassium carbonate . Meanwhile, 207 kg / h of water and 18 kg / h of ethyl ether were prepared by distillation at the top of the column. The distilled water was circulated to the R4 purifier at 35 kg / h for agitation before additional use; while 172 kg / h of remaining distilled water was used for the CO2 and NH3 T2 absorption column. The distilled ethyl ether was dispensed in the extraction column T4 for later use; while the CO2 gas discharged through the decomposition was used for acidification and crystallization in the continuous T6 crystallizer after compression. The stock solution containing a potassium carbonate solution discharged from the bottom of the column was cooled before circulating to the HCN T1 absorption column for the absorption of formonitrile.

Embodiment 5 [0047] A dosing liquid dispensing pump was used to dispense treated crystallization stock solution (10% K2CO3 solution was used in the initial start) for the HCN T1 absorption column at a flow rate of 838 kg / H. However, 5.5 kg / h of HCN gas was dispensed into the HCN absorption column for the preparation of the KCN solution in the HCN T1 absorption column, and a liquid dispensing pump was used to dispense the solution of HCN KCN to the first tubular reactor R1. A liquid dispensing pump was used to dispense ammonium bicarbonate by absorbing ammonia gas and carbon dioxide in the CO2 and NH3 T2 absorption column for the first tubular reactor R1 (16% ammonium bicarbonate solution was used in the initial start-up ) at a speed of 220 kg / h, and a liquid dispensing pump was used to supply 3-methylthio propionaldehyde to the first tubular reactor R1 at a speed of 20.8 kg / h at the same time. A reaction fluid remained

Petition 870190088055, of 9/6/2019, p. 30/38 / 25 for 3 minutes, respectively, at 60 ° C and 100 ° C, and remained for another 4 minutes at 140 ° C. The reaction fluid discharged from the first tubular reactor, R1, was subjected to decompression in the decompression tank R2 to discharge excess ammonia gas and carbon dioxide to the CO2 and NH3 T2 absorption column to obtain 1062 kg / h of 5- (β-methylthioethyl) glycolurea solution.

[0048] A liquid dispensing pump was used to dispense the 5- (β-methylthioethyl) glycolurea solution prepared for the second R3 tubular reactor, at a speed of 1.062 kg / h. A reaction fluid remained in the second tubular reactor for 9 minutes at a temperature of 190 ° C for saponification before decompression in the T3 absorption column. The gas and ammonia and carbon dioxide produced during the reaction were discharged to the CO2 and NH3 T2 absorption column for absorption. The saponification liquid was cooled to a temperature of 30 ° C in the heat exchanger, which was subsequently dispensed to the continuous extraction column T4 by means of the pump at a speed of 1.056 kg / h. Meanwhile, 1,200 kg / h of ethylene glycol dipropyl ether was dispensed to the continuous T4 extraction column for continuous reverse extraction. The continuous differential distillation of the ethylene glycol dipropyl ether layer was carried out on the T5 organic solvent recycling distillation column to recycle the solvent for use circulated during the extraction process, and incinerate waste at the same time. The water layer was dispensed to the continuous T6 crystallizer at a speed of 1.050 kg / h and, at the same time, the CO2 gas was dispensed to the continuous T6 crystallizer for acidification until the pH value of the reaction system was up to 9. Crystallization continuous was conducted at a temperature of 30 ° C, and the reaction liquid remained in the continuous crystallizer for 3 hours. The crystallization liquid was subjected to continuous solid-liquid centrifugal separation in the first solid-liquid separator S1 to filter the crude D, L-methionine product, and the mother liquor solution.

Petition 870190088055, of 9/6/2019, p. 31/38 / 25 crystallization was prepared for later use. The solid dispensing equipment was used to dispense the crude D, Lmethionine product to the R4 purifier for spiral agitation and washing in the specified amount at a rate of 35 kg / h. However, 60 kg / h of water was continuously dispensed to the R4 purifier to control the material temperature in the R4 purifier below 30 ° C. The solid material remained in the R4 purifier for 10 minutes. The intermixture subjected to continuous stirring and washing in the R4 purifier was under continuous solid-liquid centrifugal separation through the second solid-liquid separator S2. A wash filtrate was poured into the mother crystallization solution, and the D, L-methionine filter cake as filtrate was air-dried at 130 ° C under the protection of N2 to obtain 27.8 kg / h of finished D, L-methionine product. Inspection according to GBT17810-2009 Feed Grade DL-methionine was conducted to obtain the result that the methionine content was up to 99.3% and the total molar reaction yield as based on 3-methylthional propionaldehyde was up to 93, 3%.

[0049] The mother liquor solution and the wash filtrate were dispensed on the KHCO3 T7 decomposition column, at a rate of 1.106 kg / h, and remained for 3 hours at a temperature of 120 ° C to decompose the potassium hydrogen carbonate contained in the potassium carbonate stock solution. Meanwhile, 245 kg / h of water and 7 kg / h of alcohol

2-ethyl were prepared by distillation at the top of the column. The distilled water was circulated to the R4 purifier at 60 kg / h of agitation before additional use; while 185 kg / h of remaining distilled water was used in the CO2 and NH3 T2 absorption column. The alcohol

2-ethyl distillate was circulated to the T4 extraction column for later use; while the CO2 gas discharged through the decomposition was used for acidification and crystallization in the continuous T6 crystallizer after compression. The stock solution containing a carbonate solution

Petition 870190088055, of 9/6/2019, p. 32/38 / 25 potassium discharged from the bottom of the column was cooled before circulation to the HCN T1 absorption column for the absorption of formonitrile.

Claims (10)

1. Method for preparing D, L-methionine, characterized by the fact that it comprises the following steps: (1) prepare a 5- (3-methylthioethyl) glycolurea reaction fluid using 3-methylthio propionaldehyde, KCN and NH4HCO3 solutions as raw materials for continuous reaction in the tubular reactor which is gradually heated; (2) decompress the 5- (3-methylthioethyl) glycolurea reaction fluid to separate NH3 and CO2 to dispense to another tubular reactor for decomposition and saponification to obtain a saponification reaction fluid; (3) eliminate NH3 and CO2 produced during saponification by desorption of the saponification fluid to obtain a solution of D, L-methionine potassium; (4) obtain a solution of NH4HCO3 by spraying water and absorbing NH3 and CO2 when separated in steps (2) and (3), and directly use the NH4HCO3 solution as a material for preparing the reaction fluid of 5 - (3-methylthioethyl) glycolurea in step (1); (5) cool the L-methionine potassium solution in step (3), and then use an organic solvent for continuous and inverted extraction; directly using a recycled organic solvent by distilling an organic solvent layer for continuous and inverted extraction; the raffinate produced by distillation being treated as a residual fluid; (6) dispense water that is produced by continuous and countercurrent extraction in step (5) for a continuous crystallizer, simultaneously dispensing CO2 gas for the continuous crystallizer for acidification to control the pH value of the reaction fluid in the continuous crystallizer in 6- 9, and then obtain a crystallization intermixture; (7) separate solid and liquid in the crystallization intermix Petition 870190088055, of 9/6/2019, p. 34/38 2/3 to obtain crude D, L-methionine product and a mother crystallization solution; washing crude D, L-methionine product with water for solid-liquid separation to obtain a D, L-methionine filter cake and washing filtrate; (8) drying the D, L-methionine filter cake under the protection of an inert gas to obtain D, L-methionine product; (9) combining the mother liquor solution and the washing filtrate from step (7) for dispensing to a decomposition column to fully decompose KHCO3 into K2CO3 to release CO2 gas; the released CO2 gas which is subjected to compression is dispensed to the continuous crystallizer by acidification and crystallization; (10) use the stock solution containing K2CO3 as obtained in step (9) for absorbing HCN gas to prepare a solution of KCN which is the material for preparing 5- (3-methylthioethyl) glycolurea in step (1). Method for preparing D, L-methionine according to claim 1, characterized in that in step (1), a molar ratio of 3-methylthio propionaldehyde, KCN and NH4HCO3 is 1: 1-1.1: 2-3. Method for preparing D, L-methionine according to claim 1, characterized in that in step (1), a gradual heating range is 50-150 ° C with a reaction time of up to 3-15 minutes. Method for preparing D, L-methionine according to claim 1, characterized in that in step (2), the decomposition and saponification temperature is 140-220 ° C with time up to 2-15 minutes. 5. Method for preparing D, L-methionine according to claim 1, characterized in that in step (5), the temperature of the solution of D, L-methionine potassium is reduced to 0-40 ° C before using the organic solvent equivalent to 0.5-2 times the weight of the solution of D, L Petition 870190088055, of 9/6/2019, p. 35/38 3/3 potassium methionine for continuous and inverted extraction. 6. Method for preparing D, L-methionine according to claim 1 or claim 5, characterized in that in step (5), the organic solvent for continuous and inverted extraction includes one or more of toluene, ethylbenzene, dimethylbenzene , n-butyl alcohol, isobutanol, npentanol, 2-methyl-1-butanol, isoamylol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexyl alcohol, 4-methyl-2-pentanol, 2-ethyl alcohol, 2-methyl amyl alcohol, heptanol, 2-heptanol, 3-heptanol, 2-ethylhexyl alcohol, 2-octanol, octanol, 3,5,5-trimethylhexanol, methyl tert-butyl ether, isopropyl ether, n- propyl ether, n-butyl ether, isoamyl ether, hexyl ether, 2-methyl tetrahydrofuran, anisol, ethoxybenzene, 3-methylanisol, ethyl benzyl ether, ethylene glycol diethyl ether, diethylene dipropyl ether and ethylene glycol di-butyl ether. 7. Method for preparing D, L-methionine according to claim 1, characterized in that in step (6), the temperature for continuous crystallization is 0-40 ° C, while the reaction fluid remains inside the continuous crystallizer for 0.5-5 hours. 8. Method for preparing D, L-methionine according to claim 1, characterized in that in step (9), the temperature and pressure of the decomposition column are 110-160 ° C and 0.15-0.8 MPa with time of decomposition reaction up to 1-4 hours.